Exceptions in multithreaded application.

Question

I have heard from a very discerning person that an exception being thrown (and not caught) in a thread is being propagated to the parent thread. Is that true? I have tried some

Answer 1

We can use CustomExceptionHandler for this. Below code might help you.

    using System;
    using System.Threading;
    using System.Windows.Forms;

    // Create a form with a button that, when clicked, throws an exception.
     public class ErrorForm : System.Windows`enter code here`.Forms.Form
     {
        internal Button button1;

        public ErrorForm() : base()
        {
           // Add the button to the form.
           this.button1 = new System.Windows.Forms.Button();
           this.SuspendLayout();
           this.button1.Location = new System.Drawing.Point(100, 43);
           this.button1.Size = new System.Drawing.Size(75, 23);
           this.button1.Text = "Click!";
           this.Controls.Add(this.button1);
           this.button1.Click += new EventHandler(this.button1_Click);

           this.Text = "ThreadException";
           this.ResumeLayout(false);
        }

        // Throw an exception when the button is clicked.
        private void button1_Click(object sender, System.EventArgs e)
        {
           throw new ArgumentException("The parameter was invalid");
        }

        public static void Main()
        {
           // Add the event handler.
           Application.ThreadException += new ThreadExceptionEventHandler(CustomExceptionHandler.OnThreadException);

           // Start the example.
           Application.Run(new ErrorForm());
        }
     }

     // Create a class to handle the exception event.
     internal class CustomExceptionHandler
     {
         // Handle the exception event
        public static void OnThreadException(object sender, ThreadExceptionEventArgs t)
        {
           DialogResult result = ShowThreadExceptionDialog(t.Exception);

           // Exit the program when the user clicks Abort.
           if (result == DialogResult.Abort) 
              Application.Exit();
        }

        // Create and display the error message.
        private static DialogResult ShowThreadExceptionDialog(Exception e)
        {
           string errorMsg = "An error occurred.  Please contact the adminstrator " +
                "with the following information:\n\n";
           errorMsg += String.Format("Exception Type: {0}\n\n", e.GetType().Name);
           errorMsg += "\n\nStack Trace:\n" + e.StackTrace;
           return MessageBox.Show(errorMsg, "Application Error", 
                MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Stop);
        }
     }

2nd approach:-

using System;
using System.IO;
using System.Threading.Tasks;

class Example
{
   static async Task Main(string[] args)
   {
      // Get a folder path whose directories should throw an UnauthorizedAccessException.
      string path = Directory.GetParent(
                              Environment.GetFolderPath(
                              Environment.SpecialFolder.UserProfile)).FullName;

      // Use this line to throw UnauthorizedAccessException, which we handle.
      Task task1 = Task.Factory.StartNew(() => GetAllFiles(path));

      // Use this line to throw an exception that is not handled.
      // Task task1 = Task.Factory.StartNew(() => { throw new IndexOutOfRangeException(); } );
      try {
          await task1;
      }
      catch (AggregateException ae) {
          ae.Handle((x) =>
          {
              if (x is UnauthorizedAccessException) // This we know how to handle.
              {
                  Console.WriteLine("You do not have permission to access all folders in this path.");
                  Console.WriteLine("See your network administrator or try another path.");
                  return true;
              }
              return false; // Let anything else stop the application.
          });
      }

      Console.WriteLine("task1 Status: {0}{1}", task1.IsCompleted ? "Completed," : "", 
                                                task1.Status);
   }

   static string[] GetAllFiles(string str)
   {
      // Should throw an UnauthorizedAccessException exception.
      return System.IO.Directory.GetFiles(str, "*.txt", System.IO.SearchOption.AllDirectories);
   }
}